Working on an orange farm in southern Italy

Hi! this is my first post here, I've been studying permies while in the city and I'm finally able to move to the country to my husband's family land in Calabria, southern Italy.
it's 8.5 acres of orange tree plantation in an already terraced land with a tiny house at the top, we're starting to put the house in living conditions and observing what needs to be done: almost all the trees are sick because of whitefly and subsequent sooty mold, there are some olives that are sprayed two times a year because of olive fruit fly and some nuts and hazelnuts trees as canopy, we're trying to convince my husband's family to try a permaculture approach instead of the tractor, stilling and spraying that they have been doing, we're planing on planting flowering plants (nastritums, marry golds) and mediterranean plants (rosemary, mint, lavander, oregano, broom and others) to help with the fly pests.
The soil is sandy-conglomerate from the Pleistocene (very fine sandy soil, powderlike, with not much drainage and lots of sea shells), and when rain comes, we have landslides problems, there are some very steep vertical walls where nothing is growing and I don't know how to start plants there, if anyone has any advise on this or the above mentioned issues, I would be very thankful since we're on the design part of the process, we would also like to make a water system that flows all over the land but we're not sure how to do it without creating further landslides (we were mainly thinking in planting trees with deep roots to create support and some deep root plants to hold the hills)